Hydraulic drawbench



June 29, 1965 G. A. MITCHELL 3,191,409

HYDRAULIC DRKWBENQH 4 Sheets-Sheet 1 7 Filed April 10. 1961 L mm mm m m 6 rrakl/sf June 29, 1965 G. A. MITCHELL 3,191,409

HYDRAULIC DRAWBENCH Filed April 10, 1961 v 4 Sheets-Sheet 2- III II I

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BY7MW June 29, 1965 G./-\- MITCHELL HYDRAULIC DRAWBENGH 4 Sheets-Sheet 3 Filed April 10. 1961 INVENTOR. 650m 4. @ITc/ASLL. 8Y7 277 Adm.

June 29, 1965 G. A. MITCHELL 3,191,409

HYDRAULIC DRAWBENCH Filed April 10. 1961 4 Sheets-Sheet 4 RESLRVOLE K INVEN TOR. 65026.5 6 0717-00544 av7ig United States Patent 3,191,409 HYDRAULIC DRAWBENCH George A. Mitchell, Youngstown, Ohio, assignor, by

mesne assignments, to Lombard Corporation, Youngstown, Ohio, a corporation of Ohio Filed Apr. 10, 1961, Ser. No. 101,715 4 Ciaims. (Cl. 7214) This invention relates to drawbenches adapted to draw tubes and the like through a die, and more particularly to a drawbench'of the type described in which the prime mover for the draw carriage is a fluid motor.

As is well known, a conventional mechanical drawbench employs, as a basic component, a circular die through which a workpiece is drawn inorder to elongate it and reduce its diameter. In the case where a tube is being drawn, the tube is first loaded onto a mandrel which extends parallel to the central axis of the die on one side thereof. The mandrel forwards a reduced diameter end of the tube into the die, and this end is engaged by gripper jaws carried on a draw carriage or dolly which travels on a track extending parallel to the central axis of the die on the side opposite the mandrel. In the usual case, the draw carriage engages one or more chains which force it along its track outwardly and away from the die, thereby pulling the tube through the annular opening defined between the periphery of the die and the periphery of the mandrel.

Although mechanical drawbenches of the type described above have won general acceptance and are useful in many applications, they have certain inherent disadvantages. For example, one such disadvantage resides in the fact that pulsations in drawing speed occur as the chain or chains articulate over their drive sprockets; and as the capacity of the bench increases, thus requiring a larger chain, this pulsating efiect is accentuated.

Another disadvantage of mechanical benches is due to the fact that they require a rather complicated arrangement for controlling movement of the draw carriage along its track. That is, the draw carriage must either be connected to the draw chains by means of hook, devices which automatically retract when the carriage is not under tension, or by hook devices which are permanently connected to the chains. In the former case, the drive chains move continuously in one direction, meaning that a separate return chain must be provided to return the draw carriage to the die at the completion of a drawing operation. In the latter case, the chain drive must be made reversible to return the draw carriage to the die'; and this, in turn, requires an expensive and complicated direct current motor control for the'chain drive motor. In both cases, it is difficult to stop the drawing operation before its completion to examine the progress and quality of the drawn workpiece as may be required, for example, in the case where expensive alloys are being drawn.

Probably one of the most serious problems encountered with mechanical benches is due to the fact that, the workpiece or workpieces will jump forwardly with considerable force as the trailing ends thereof pass through the dies, the obvious reason being that the workpieces are under substantial tension during the drawing operation, and the sudden release of such tension is accompanied by a release of energy which propels them forwardly with considerable force. This is a serious problem, particularly in the case where thin-walled tubes are being drawn, in that the forward ends of the tubes are kinked, bent or twisted out of shape due to the sudden shock of abruptly striking the draw carriage as they leave the gripper jaws. Furthermore, the problem of kinked, bent or twisted material becomes more acute with double and triple drawing operations as the draw carriage is heavier and will not Ice run away when it receives the shock of the material being drawn, which in turn causes it to kink more than with a single draw. Various devices have been devised for expending the kinetic energy of the tube such as shock absorbers, deflectors and other similar devices; however, all of these devices complicate the construction of the draw carriage.

Finally, a disadvantage of mechanical drawbenches resides in the fact that, as a practical matter, the maximum drawing force which they can achieve does not exceed about 300,000 pounds. Larger drawing forces would require extremely expensive and bulky draw chains, sprockets and associated gear drive apparatus. Furthermore, where the material being drawn is such that a single constant speed of the draw carriage cannot be tolerated, a chain drawbench, even one requiring a maximum force below 300,000 pounds, would require a very expensive electrical control system to start and stop the draw chains.

As an overall object, the present invention seeks to provide a new and improved drawbench arrangement which overcomes the foregoing disadvantages and others.

More specifically, an object of the invention is to provide a drawbench in which the draw carriage is actuated by means of a fluid motor, preferably a hydraulic cylinder and piston arrangement, which serves the dual function of pulling the draw carriage away from the die of the drawbench during a drawing operation, and also serves to return the draw carriage to the die at the completion of a draw. 7

Another object of the invention is to provide a hydraulically-actuated drawbench in which the speed of the draw carriage may be varied through a wide range to accommodate different types of materials being drawn.

Still another, and most important, object of the invention is to provide a drawbench arrangement in which the problem of kinked or bent workpiece end is eliminated without requiring complicated shock absorbers, deflectors and other similar devices on the draw carriage.

As will hereinafter become apparent, the drawbench of the invention is similar to conventional drawbenches in that it comprises at least one die having a mandrel on one side thereof and a track structure on the other side extending parallel to the central axis of the die. Positioned on the track structure, as in a conventional drawbench, is a drawcarriage having gripper jaws thereon which engage a tube or other workpiece which projects through the die and pulls this workpiece through the die for the purpose of elongating the same and reducing its cross-sectional area.

In the case of the present invention the motive force for the draw carriage is supplied by means of a fluid motor which, in the embodiment of the invention shown herein, comprises a hydraulic cylinder and piston arrangement positioned at the end of the aforesaid track structure opposite the die. Interconnecting the piston of the cylinder and the draw carriage is a piston rod, the arrangement being such that the cylinder may be pressurized in one direction to pull workpieces through the die or alternatively pressurized in the opposite direction to return the draw carriage to the die preparatory to a succeeding drawing operation. The opposite ends of the cylinder are "connected to the output ports of a reversible, variable displacement pump which may selectively apply fluid under pressure to either end of the cylinder, and which may be operated to gradually increase its output pressure in either direction from zero up to a maximum limit. Thus, the drawing operation may be started gradually rather than abruptly as in the case of a mechanical bench, and the. draw carriage may be easily stopped at any point along the draw by reducing the pump output pressure to zero.

An unexpected advantage of a hydraulic drawbench of this type is due to the fact that tubular workpieces, when they leave the gripper jaws in the draw carriage, are not kinked or bent, notwithstanding the fact that no shock absorbers, deflectors or other similar means are employed. No explanation can be givn for this result since it would logically be assumed that the tubes, having the same tension or kinetic energy as those drawn on a mechanical bench, would be driven against the draw carriage with resultant damage to their ends. Furthermore, the elimination of bent or kinked ends prevails even in the case where a plurality of tubes are drawn and certain of those tubes leave the dies while other tubes are still in tension, meaning that the draw carriage cannot move backwardly under the impact of the tube to absorb its kinetic energy. Thus, the invention provides an unexpected result which is highly beneficial and eliminates the waste attendant to mechanical drawbenches due to damaged ends.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drhawlilngs which form a part of this specification, and in w 1c FIGURE 1 is a top or plan view of the overall hydraulic drawbench arrangement of the invention;

FIG. 2 is a side or elevational view of the apparatus shown in FIG. 1;

. 4 cated at 40. Supported above the forward end of cylinder 38 on platform 42 is a reversible, variable displacement hydraulic pump 44 which is driven by an electric motor 46. As will be seen, the pump 44 serves to pressurize the cylinder 38 in one direction or the other to move the draw carriage 34 toward or away from the die stand 10. v 7

Referring now to FIGS. 3 and 4,. the die stand 10 comprises a pair of triangularly shaped side plates 48 and 50 which give lateral support to a pair of upright members 52 and 54. The members 52 and 54 are provided with vertical slots 56 which receive a die block 60. Provided in the die block 60 are three spaced openings or holes 62 (FIG. 4), each of which receives a die assembly 64.

Pivotally connected to the opposite side plates 48 and 50 are arms 72 and 74 which support a grooved roller 76, the purpose of this roller being to support and guide the tubes as they pass through the die during a drawing operation. As shown, the arms 72 and 74 are interconnected by means of an angle 78 provided with a pair of adjusting screws 80 which may be used in an obvious manner to vary the height of the grooved roller 76 for various tube diameters.

FIG. 3 is a partially broken-away top view of the draw Q carriage, die stand andforward end of the mandrel assembly of the hydraulic drawbench of the invention;

FIG. 4 is a partially broken-away side view of the apparatus shown in FIG. 3;

FIG. 5 is a cross-sectional view of the tube storage rack and track assembly of the drawbench taken substantially along line V-V of FIG. 2; and

FIG. 6 is a schematic diagram of the hydraulic and electrical circuits for the drawbench of the invention.

Referring now to the drawings, and particularly to FIGS. 1 and 2, the numeral 10 designates a die stand carried at one end of a mandrel supporting table12. The mandrel supporting table 12 extends parallel to the axes of dies carried within the die stand 10 and comprises an elongated structural member 14 such as a channel carried on a plurality of spaced stands 16, substantially as shown. Supported on the right end of member 14, as shown in FIGS. 1 and 2, is a mandrel manipulating mechanism 18 which comprises a short stroke hydraulic cylinder 20 having its piston rod connected to a reciprocable actuating block 22. Pivotally carried on the actuating block 22 are a plurality of mandrel rods 24, hereinafter described indetail. The forward or left ends of the mandrel rods as shown in FIGS. 1 and 2 are supported on a cradle or roller which is pivotally connected through linkages 26 to the member 14. These linkages are actuated by means of a hydraulic cylinder 28 to either lower or elevate the ends of the mandrel rods. In this manner, the mandrel rods 24 may be elevated by means of linkages 26 and cylinder 28 into alignment with a rack 30 as shown by the dotted outline in FIG. 2 where tubes are loaded onto the mandrels. Thereafter, the mandrel rods are lowered by the linkages 26 and cylinder 28 into alignment with the dies carried within die block 10 preparatory to a drawing operation. Actually, two such sets of linkages 26 and cylinders 28 are provided to elevate the mandrel rods, the second set being absent in FIGS. 1 and 2 due to the broken section showing.

Movable along the track structure 32 is a draw carriage, generally indicated at 34. The draw carriage 34 is connected as shown through an elongated piston rod 36 to a piston, not shown, reciprocably carried within a hydraulic cylinder 38 which is in general alignment with the axes of the dies in die stand 10 at the end of track structure 32 opposite the die stand. As shown, the cylinder 38 is carried on a supporting structure, generally indi- The mandrel rods 24 are each provided with an enlarged head 82 and are carried within tubular members 84. As was previously explained, the other end of each of the mandrel rods 24 is pivotally connected to the actuating block 22 shown in FIGS. 1 and 2 whereby the forward ends of the mandrel rods and the enlarged heads 82 thereon may be elevated above the die structure 10 to receive tubes to be drawn and thereafter lowered into alignment with the dies 64. To elevate, the forward ends of the mandrel rods, apparatus including the hydraulic cylinders 28 and linkages 26 is provided. The cylinders are supported by means of plates 86 on the mandrel supporting table 14 and have their piston rods pivotally connected as at 88 to bars 90 which extend between and are connected to the pivot arms 26'on either side of the mandrel supporting table 14. Carried between the forward ends of the pivot arms 26 are grooved rollers 92, similar to the grooved roller 76 already described, which support the forward ends of the tubular members 84. Extending upwardly from either end of the rollers 92 are a pair of arms 94 having rods 96 extending between their upper extremities for the purpose of limiting upward movement of the tubular members 84 and the mandrel rods 24 carried thereby.

With the arrangement shown, the cylinders 28 may be pressurized in one direction to elevate the mandrel rods into tube receiving position and thereafter pressurized in the opposite direction to lower the mandrel rods into alignment with the dies 64. After the mandrel rods have been loaded with tubes and the pivot arms 26 lowered, the short stroke cylinder 20 (FIGS. 1 and 2) in the mandrel manipulating mechanism 18 will be pressurized to force the mandrel rods and the tubes carried thereby to the left as shown in FIGS. 3 and 4 whereby previously swaged or reduced diameter ends of the tubes will be forced through the dies 64.

Referring, now, to the draw carriage 34, it comprises a pair of side plates 98 and 100 which are interconnected by means of a pair of blocks 102 and 104. The block 104 comprises a gripper head having three sets of converging guide slots formed therein, only one of said sets being shown in FIG. 3. Received within the converging guide slotsare a pair of stock-engaging grip bits and 112, the arrangement being such that upon forward movement of the grip hits the same are caused to converge while upon rearward movement they are caused to diverge. The guide slots are open as at 108 (FIG. 5) at the lower side of the gripper head 104 to permittubes to drop out of the interstice formed between the slots at the completion of a drawing operation. Each of the bits 110 and 1 12 is provided with a transverse slot in its upper'surface for the reception of transverse arm portions of a slide block plunger 118 carried within a cooperating bore provided in the block 102. As shown, the piston 118 is provided with a head portion 120 which engages a cooperating slot in the slide block 116. A coil spring 122 interposed between a shoulder in the bore and an enlarged head on the back of the piston 1-1'8 serves to normally retain the piston in retracted position whereby the slide block 116 will be moved to the left as shown in FIG. 3 to cause the grip bits 110 and 112 todiverge. A transversely-extending passage 126 is provided in the block 102 for conducting compressed air into the bores provided for the respective pistons 11 8. Upon the introduction of compressed air into the bores, the pistons 118 will be forced to the right as shown in FIG. 3, thereby causing the grip bits 110 and 1-12 associated with each piston to converge. Above the slide blocks 1.16 is positioned a removable plate 128 carried on a pair of pivoted arms 130 and 132,

Connected to the block 102 is the piston rod 36 for hydraulic cylinder 38, the arrangement being such that the cylinder may be pressurized to move the draw carriage .along the track structure 32. For guiding the draw carriage along the track structure, rollers 134 are provided at the bottoms of plates 98 and 100. In addition, plates 136 are bolted to each of the plates 98 and 100 and carry rollers 1138 which engage the bot-tom of the track structure as well as lateral guiding rollers 140 which engage the sides of the track structure.

The details of the track structure 32 are shown in FIG. 5. It comprises an inverted channel section 142 having guideways 144 formed therein for the reception of rollers 134 on the draw carriage 34. The channel 142, in turn, is welded or otherwise securely fastened to one leg of each of two angles 146 and 148, the other legs of which are supported on spaced supporting stands 150. As shown, the rollers .138 on the draw carriage 34 engage the lower surfaces of the angles i146 and 148; whereas the rollers 140 engage the sides of these same angles, In order to direct the drawn tubes into a receiving bin to the left of the track structure as shown in FIG. 5, a plurality of triangularly shaped plates 1152 are spaced along the track structure 32 such that When the newly-drawn tubes drop out of the gripper jaws, they will drop onto the plates 152 and roll to the left as shown in FIG. 5.

The tube storage rack '30 shown in FIGS. 1 and 2 is formed from a plurality of spaced structures, one of which is shown in FIG. 5. It comprises a supporting stand 154 which carries a horizontallyextending beam #156 having short side supporting sections 158 and 160 extending upwardly from either end. Secured to the support 160 on each of the stands is a U-shaped bracket 162. These brackets, taken along the length of the rack, form a rod supply bin. Supported on the horizontally-extending member 156 of each of the supporting stands is a plywood sheet or the like 164; and this sheet, in effect, forms the tube receiving rack from which tubes are loaded onto the mandrels 24 when the forward ends of such mandrels are elevated by the cylinders 28 shown in FIG. 4.

Referring now to FIG. 6, it can be seen that the reversible, variable displacement pump 44 has an input port- 166 connected through conduit 168 to a fluid reservoir 17%] and a pair of output ports 172 and 174. The pump 44 may be of the general type shown in US. Patent No. 2,737,895, 2,577,242 or 2,767,894. A pump of this type may be adjusted to deliver fluid from either one of the output ports 172 or 174. Furthermore, with the motor 46 operating at constant speed, the supply of fluid volume from the pump may be increased from zero up to a predetermined maximum limit from either one of the output ports. For example, fluid under pressure may be delivered from output port 174, and under these circumstances fluid will flow into port .172. On the other hand, when the direction of fluid flow through the pump is reversed, the output will be from port 172 while fluid will fio-w into port 174.

Included in the hydraulic circuit for the pump 44 is a fluid pressure operated valve 176 having a valve member 178 therein, a pair of input ports i180 and 182, and a pair of output ports 184 and 186. Connected to fluid pressure chambers at the opposite ends of valve member 178 is a first conduit 188 connected to output port 172 of pump 44 and a second conduit 190 connected to output port 174 of the pump. In this manner, when the pump is delivering fiu-id from port 172, pressure will be delivered through conduit 1188 to move the valve member to the left and into the position shown in FIG. 6. Under these conditions, input port 182 will be connected to output port 1184, and input port 180 will be connected to output port 186. When, however, the direction of fluid flow through pump 44 is reversed and fluid is being delivered from port 174, fluid under pressure will be delivered through conduit 190 to the opposite ends of valve member 178 whereby this valve member will be shifted to the right from the position shown in FIG. 6. Under these conditions, input port .180 will be connected to output port 184; whereas input port 182 will 'be connected to output port 186.

As shown, the output port 174 of pump 44 is connected through conduit 192 to input port 180 of valve 176 as well as the end of cylinder 38 opposite the piston rod 36. The output port 1172 of the pump 44, on the other hand, is connected through conduit 194 to the input port 182 of valve 176 and also through conduit 195 and a high pressure relief valve 196 to the reservoir 170. Gutput port 186 of valve 176 is connected through check valve 198 to reservoir 170, and out-put port 184 is connected through conduit 200 to the forward end of cylinder 38 as shown. Connected to conduit 1194 is an electrical pressure switch 202 which will close its contacts in response to an increase in the pressure output from port 172.

The pump 44 is controlled by three solenoids 204, 206 and 208. Solenoid 208, when energized, will cause the pump to deliver its full volumetric output from port 172. Solenoid 204, when energized, will cause the pump to deliver its full volumetric output from port 174; and solenoid 206, when energized, will cause the pump 44 to deliver a reduced volumetric output from port 174. When none of the solenoids 204-208 are energized, the pump will be in neutral position at which time pressure will flow from neither of the ports 172 and 174.

Along the path of draw carriage 34 on track 32 are three limit switches 210, 212 and 214. Limit switch 210 is located immediately adjacent the end of cylinder 38 and is provided with a pair of normally closed contacts 216. Limit switch 214 is located immediately adjacent the die stand 10 and is provided with a pair of normally closed contacts 218 and a pair of normally open contacts 220; while limit switch 212 is located slightly ahead of limit switch 214 and is provided with a pair of normally closed contacts 222 and a pair of normally open contacts 224.

The circuit for controlling the solenoids 204-208 is connected to the positive and negative terminals of a source of voltage, not shown, as at 226, 228 and 230. This circuit includes three relays 232, 234, and 236. Relay 232 has a single pair of normally open contacts 238 and is adapted to be energized to close these contacts when the pressure switch 202 is actuated to close its contacts. Relay 234 is provided with two sets of normally open contacts 240 and 242; whereas relay 236 is provided with pairs of normally closed contacts 244 and 246 and pairs of normally open contacts 248 and 256. A normally open pushbutton switch 252, when depressed, will energize the circuit to return draw carriage 34 to the die stand 10; whereas a normally closed pushbutton switch 254 may be depressed to stop the draw carriage at any point as it moves away from the die stand 10. If it is desired to operate the drawbench in an automatic basis, a switch 256 will be closed; whereas if it is desired to manually operate the bench, the switch 256 will be opened, whereupon the draw carriage 34 may be actuated by manually depressing a normally open pushbutton switch 258.

In operation, it will be assumed initially that none of the solenoids 204-208 are energized and that the draw carriage 34 is stopped along the track 36 with no tubes held in the grip bits 100 and 112 (FIG. 3). In order to return the draw carriage 34 to the die stand 10, the pushbutton 252 is depressed. This completes a circuit to the energizing coil of relay 234 through the switch 252 and the normally closed contacts 246 of relay 236 which is now deenergized. When relay 234 thus becomes energized, its contacts 240 will close, thereby completing a holding circuit for the energizing coil of the relay through contacts 240, the normally closed contacts 218 of limit switch 214 and pushbutton switch 254. With relay 234 energized, the contacts 242 will also close, thereby completing a circuit to solenoid 204 through the contacts 242 and the normally closed contacts 222 of limit switch 212. With solenoid 204 energized, the pump 44 will now deliver full volumetric output from port 174, thereby causing the valve member 178 to shift from left to right as shown in FIG. 6 whereby port 180 is connected to port 184 while port 182 is connected to port 186. The piston within cylinder 38 will thus be forced to the right as shown in FIG. 6 to move the draw carriage 34 toward the die stand 10. It will be noted that the right end of cylinder 38 is connected to conduit 192 through conduit s and ports 184 and 180 of valve 176 during this time. However, due to the fact that the piston rod 36 is within the right end of cylinder 38, the total pressure on the left side of the piston will be greater than that on the right side, and fluid will be expelled from the right side through conduit 200 and valve 176 to conduit 192 where it will be added to the fluid delivered from pump 44. Initially, with solenoid 204 energized, the rate of fluid flow to the left side of cylinder 38 will be high so that the travel of the draw carriage will be rapid from left to right as shown in FIG. 6. If this rapid movement were permitted to continue as the draw carriage approached the die stand 10, the result might bedamage to the die block structure. Accordingly, as the draw carriage 34 approaches the diestand 10, it will first trip the limit switch 212. With limit switch 212 tripped, contacts 222 open while contacts 224 close. Solenoid 204 thus becomes deenergized while solenoid 206 becomes energized through a circuit including the contacts 224 of limit switch212, the contacts 242 of relay 234, which is now energized, and the contacts 244 of relay 236, which is now deenergized. Thus, energization of solenoid 206 decreases the volumetric output of the pump from port 174 which results in a deceleration of the draw carriage 34.

As the draw carriage 34 moves further to the right, it will finally trip limit switch 214. With the switch 256 for automatic operation closed, the relay 236 will now become energized through a circuit including switch 256, contacts 220 of limit switch 214 and pushbutton switch 254. At the same time, since the contacts 218 of limit switch 214 open, the circuit to the energizing coil of relay 234 is broken so that the relay becomes deenergized to open its contacts 240 and 242.

When limit switch 214 is tripped, means, not shown, will inject fluid under pressure into passage 126 in draw carriage 34 (FIG. 3) to cause the grip bits 110 and 112 to converge on the swaged or reduced diameter ends of tubes to be drawn which extend through the dies 64. In this manner, the ends of the tubes are securely gripped by the bits and will be pulled through the dies 64 when the draw carriage 34 moves to the left as shown in FIGS. 3, 4 and 6. 7

When relay 236 is energized upon closure of contacts 220 of limit switch 214, its normally open contacts 248 and 250 will close. A circuit is now completed to solenoid 208 on pump 44 through the contacts 250 and the normally closed contacts 216 of limit switch 218. Under these conditions, the full volumetric output of the pump 44 is delivered from port 172 to shift the valve member 178 into the position shown in FIG. 6 wherein input port 180 is connected to output port 186 and input port 182 is connected to output port 184 and conduit 200. Thus, fluid under pressure is now delivered through conduit 194, the valve 176 and conduit 200 to the right side of cylinder 38 to move the draw carriage 34 away from the die stand 11 As soon as pressure builds up in conduit 194, the pressure switch 202 will be actuated to complete a circuit to relay 232. This energizes the relay and closes its contacts 238. Thus, even though contacts 220 open when the draw carriage moves away from the die stand 10, an energizing circuit will still be completed to relay 236 through pushbutton switch 254, contacts 248 of relay 236 and contacts 238 of relay 232, these latter contacts being closed at this time due to the actuation of pressure switch 202.

As soon as the draw carriage 34 moves away from the die stand 10, the fluid pressure in passage 126 (FIG. 3) will be released, however the grip bits 118 and 112 will still securely grip the ends of the tubes being drawn due to the tension in these tubes which causes the grips to further converge.

With relays 232 and 236 energized, the draw carriage will continue to move to the left as shown in FIG. 6 to pull the tubes through the dies in die stand 10. However, the draw may be stopped at any point by depressing the pushbutton switch 254 which breaks the circuit to relay 236, thereby causing contacts 250 to open and break the circuit to solenoid 208. To again start the draw carriage 34, the pushbutton 254 is released and pushbutton 258 is depressed to energize solenoid 236 and close contacts 258. By the time the pushbutton 258 is released, the pressure will have built up in conduit 194 to close pressure switch 202 whereby relay 232 will be energized to close contacts 238 and provide a holding circuit for relay 236 through contacts 238 and 248. Movement of the drawcarriage 34 to the left will continue until all of the tubes have been pulled through their associated dies.

Since the volume of cylinder 38 to the left of its piston is greater than that to the right of the piston, some means must be provided to expel the excess liquid from the system during the power stroke when the draw carriage 34 is moving to the lefta-s shown in FIG. 6. For this purpose, the conduit 192 is now connected through valve 176 and check valve 198 to reservoir 17%, the arrangement being such that the excess liquid will pass through the check valve 198 and into the reservoir. This action will continue with the draw carriage 34 moving to 'the left while pulling the tubes through the die 78.

Check valve 196 merely serves to prevent an excess build up of pressure in conduit 194. As the trailing end of each tube passes through its associated die, it Will snap forwardly, thereby forcing the grip bits and. 112 to diverge and permit the drawn tube to fall onto plates 152 (FIG. 5) where it rolls out onto a receiving rack, not shown.

Movement of the draw carriage 34 to the leftas shown in FIG. 6 will continue until the last tube passes through its associated die and drops onto plates 152, whereupon the pressure in conduit 194 will decrease to open pressure switch 282 and deenergize relay 232. With relay 232 deenergized, the contacts 238 will open to break the holding circuit to relay 236. Consequently, relay 236 now becomes deenergized and contacts 250 open to break the circuit to solenoid 288 on pump 44. The pump now assumes a neutral position wherein fluid pressure is delivered from neither one .of the, ports 172 and 174 while draw carriage 34 is stopped. To return the draw carriage to the die stand 10, the pushbutton switch 252 is depressed, whereupon the foregoing cycle of operation is repeated.

If it should happen that the length of the tubes being drawn is such that the draw carriage 34 will not stop before reaching the right end of cylinder 38, the limit switch 216 will be tripped to break the circuit to solenoid 208, thereby preventing the draw carriage from ramming into the end of the cylinder. From this point, the draw carriage may again be returned to the die stand 10 by merely depressing the pushbutton switch 252.

In the foregoing cycle of operation, the drawing operation was automatic. If, however, it is desired to control the drawing operation manually, the switch 256 may be opened. Under these circumstances, the draw may be started and stopped at will by the operator by merely depressing the pushbutton switch 258 to selectively energize relay 236 to close its contacts 250 and complete the circuit to solenoid 208. In this latter case, however, the limit switch 210 still serves to break the circuit to the solenoid 208 in the event that the draw carriage 34 moves too far to the left.

It is important to note that in the present invention, no shock absorbers, deflectors or other similar means are provided in connection with the grip bits 110 and 112 for the purpose of absorbing the shock of the tube at the completion of a drawing operation. As was mentioned above, in a mechanical bench tubes jump forwardly at the completion of a draw and strike the slide block 116. If there is no provision for shock absorbers or deflectors in a mechanical bench, the impact of the newly-drawn tube against the slide block will kink or bend the forward end of the tube. In the present invention, however, such devices are entirely unnecessary and the tubes drop out of the grip bits 110 and 112 dead. This, of course, is a highly valuable advantage of the present invention since it positively eliminates damage to tube ends and also eliminates the shock absorbing or deflecting apparatus which would otherwise be required.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. A drawbench assembly comprising a die through which workpieces are drawn, a track structure extending parallel to the central axis of said die on one side of the die, a draw carriage movable along said track structure and adapted to pull workpieces through the die, fluid motor means for moving the draw carriage away from the die and for returning the draw carriage to the die at the completion of a drawing operation, said fluid motor means including a cylinder having a piston reciprocable therein, means operatively connecting said piston to the draw carriage whereby movement of the piston in one direction will cause the draw carriage to move away from the die While movement of the piston in the opposite direction will cause the draw carriage to move toward the die, a fluid reservoir, a pump having an input port connected to said reservoir and a pair of output ports, means connecting the respective output ports to opposite ends of said cylinder, means including a first electromechanical device electrically actuable to cause said pump to deliver fluid under pressure from said first port to one end of the cylinder to cause the draw carriage to move away from said die, means including a second electromechanical device electrically actuable to cause said pump to deliver fluid under pressure from said second port to the other end of the cylinder to cause the draw carriage to move toward said die, means including a third electromechanical device electrically actuable to cause the pump to deliver a rate of fluid flow from said first port which is less than that delivered when the first electromechanical device is actuated, load responsive switch means actuable when fluid under pressure is delivered from said first port as the draw carriage moves away from the die and pulls a workpiece through the die, a first limit switch device positioned along the track structure immediately adjacent said die and actuable by the draw carriage at its extreme limit of travel along the track structure toward the die, a second limit switch device positioned along the track structure ahead of the first limit switch device and actuable by movement of the draw carriage as it approaches the die but before the draw carriage reaches its extreme limit of travel adjacent the die, first electrical circuit means including the first limit switch device for actuating said first electromechanical device to initially cause the pump to deliver fluid under pressure from said first port when the first limit switch device is actuated and the draw carriage is at its extreme limit of travel adjacent the die, second circuit means including said pressure responsive switch means for actuating said first electromechanical device to cause the pump to continue to deliver fluid under pressure from said first port when the load responsive switch means is actuated upon delivery of fluid under pressure from said first port and for deactuating the first electromechanical device to stop the flow of fluid under pressure from said first port when the pressure at said first port drops at the completion of a drawing operation as the trailing end of a workpiece passes through said die, third circuit means for actuating said second electromechanical device after the completion of a drawing operation to cause said pump to deliver fluid from said second port and thereby cause the draw carriage to travel toward said die, and fourth circuit means including said second limit switch device for actuating said third electromechanical device as the draw carriage approaches the die to thereby decrease the rate of fluid flow from said second port and reduce the rate of travel of the draw carriage toward the die.

2. A drawbench assembly comprising a die through which workpieces are drawn, a track structure extending parallel to the central axis of said die on one side of the die, a draw carriage movable along said track structure and adapted to pull workpieces through the die, fluid motor means for moving the draw carriage away from the die and for returning the draw carriage to the die at the completion of a drawing operation, said fluid motor means including a cylinder having a piston reciprocable therein, means operatively connecting said piston to the draw carriage whereby movement of the piston in one direction will cause the draw carriage to move away from the die while movement of the piston in the opposite direction will cause the draw carriage to move toward the die, a fluid reservoir, a pump having an input port connected to said reservoir and a pair of output ports, means connecting the respective output ports to opposite ends of said cylinder, means including a first electromechanical device electrically actuable to cause said pump to deliver fluid under pressure from said first port to one end of the cylinder to cause the draw carriage to move away from said die, means including a second electromechanical device electrically actuable to cause said pump to deliver fluid under pressure from said second port to the other end of the cylinder to cause the draw carriage to move toward said die, means including a third electromechanical device electrically actuable to cause the pump to deliver a rate of fluid flow from said first port which is less than that delivered when the first electromechanical device is actuated, load responsive switch means actuable when fluid under pressure is delivered from said first port as the draw carriage moves away from the die and pulls a workpiece through the die, a first limit switch device positioned along the track structure immediately adjacent said die and actuable by the draw carriage at its extreme limit of travel along the track structure toward the die, a second limit switch device positioned along the track structure ahead of the first limit switch device and actuable by movement of the draw carriage as it approaches the die but before the draw carriage reaches its extreme limit of travel adjacent the die, a first relay device energizable when the first limit switch device is actuated, a second relay device energized when the load responsive switch means is actuated, a holding circuit operable to energize said first relay device when the second relay device is energized regardless of whether the first limit switch device is actuated, a third relay device energizable only when the first relay device is deenergized, first circuit means for actuating said first electromechanical device when the first relay device is energized, second circuit means for actuating said second electromechanical device when said second limit switch device is deactuated and the third relay device is energized, and third circuit means for energizing said third electromechanical device when the second limit switch device is actuated and the third relay device is energized.

References Cited by the Examiner UNITED STATES PATENTS 2,258,886 10/41 Ernst 60-52 2,446,438 8/48 Strock 205-3 2,597,623 5/52 Dies et al 2055 CHARLES W. LANHAM, Primary Examiner. LEON PEAR, Examiner. 

1. A DRAWBENCH ASSEMBLY COMPRISING A DIE THROUGH WHICH WORKPIECES ARE DRAWN, A TRACK STRUCTURE EXTENDING PARALLEL TO THE CENTRAL AXIS OF SAID DIE ON ONE SIDE OF THE DIE, A DRAW CARRIAGE MOVABLE ALONG SAID TRACK STRUCTURE AND ADAPTED TO PULL WORKPIECES THROUGH THE DIE, FLUID MOTOR MEANS FOR MOVING THE DRAW CARRIAGE AWAY FROM THE DIE AND FOR RETURNING THE DRAW CARRIAGE TO THE DIE AT THE COMPLETION OF A DRAWING OPERATION, SAID FLUID MOTOR MEANS INCLUDING A CYLINDER HAVING A PISTON RECIPROCABLE THEREIN, MEANS OPERATIVELY CONNECTING SAID PISTON TO THE DRAW CARRIAGE WHEREBY MOVEMENT OF THE PISTON IN ONE DIRECTION WILL CAUSE THE DRAW CARRIAGE TO MOVE AWAY FROM THE DIE WHILE MOVEMENT OF THE PISTON IN THE OPPOSITE DIRECTION WILL CAUSE THE DRAW CARRIAGE TO MOVE TOWARD THE DIE, A FLUID RESERVOIR, AND A PAIR OF OUTPUT PORT CONNECTED TO SAID RESERVOIR AND A PAIR OF OUTPUT PORTS, MEANS CONNECTING THE RESPECTIVE OUTPUT PORTS TO OPPOSITE ENDS OF SAID CYLINDER, MEANS INCLUDING A FIRST LEECTROMECHANICAL DEVICE ELECTRICALLY ACTUABLE TO CAUSE SAID PUMP TO DELIVER FLUID UNDER PRESSURE FROM SAID FIRST PORT TO ONE END OF THE CYLINDER TO CAUSE THE DRAW CARRIAGE TO MOVE AWAY FROM SAID DIE, MEANS INCLUDING A SECOND ELECTROMECHANICAL DEVICE ELETRICALLY ACTUABLE TO CAUSE SAID PUMP TO DELIVER FLUID UNDER PRESSURE FROM SAID SECOND PORT TO THE OTHER END OF THE CYLINDER TO CAUSE THE DRAW CARRIAGE TO MOVE TOWARD SAID DIE, MEANS INCLUDING A THIRD ELECTROMECHANICAL DEVICE ELECTRICALLY ACTUABLE TO CAUSE THE PUMP TO DELIVER A RATE OF FLUID FLOW FROM SAID FIRST PORT WHICH IS LESS THAN THAT DELIVERED WHEN THE FIRST ELECTROMECHANICAL DEVICE IS ACTUATED, LOAD RESPONSIVE SWITCH MEANS ACTUABLE WHEN FLUID UNDER PRESSURE IS DELIVERED FROM SAID FIRST PORT AS THE DRAW CARRIAGE MOVES AWAY FROM THE DIE AND PULLS A WORKPIECE THROUGH THE DIE, A FIRST LIMIT SWITCH DEVICE POSITIONED ALONG THE TRACK STRUCTURE IMMEDIATELY ADJACENT SAID DIE AND ACTUABLE BY THE DRAW CARRIAGE AT ITS EXTREME LIMIT OF TRAVEL ALONG THE TRACK STRUCTURE TOWARD THE DIE, A SECOND LIMIT SWITCH DEVICE POSITIONED ALONG THE TRACK STRUCTURE AHEAD OF THE FIRST LIMIT SWITCH DEVICE AND ACTUABLE BY MOVEMENT OF THE DRAW CARRIAGE AS IT APPROACHES THE DIE BUT BEFORE THE DRAW CARRIAGE REACHES ITS EXTREME LIMIT OF TRAVEL ADJACENT THE DIE, FIRST ELECTRICAL CIRCUIT MEANS INCLUDING THE FIRST LIMIT SWITCH DEVICE FOR ACTUATING SAID FIRST ELECTROMECHANICALCAL DEVICE TO INITIALLY CAUSE THE PUMP TO DELIVER FLUID UNDER PRESSURE FROM SAID FIRST PORT WHEN THE FIRST LIMIT SWITCH DEVICE IS ACTUATABLE AND THE DRAW CARRIAGE IS AT ITS EXTREME LIMIT OF TRAVEL ADJACENT THE DIE, SECOND CIRCUIT MEANS INCLUDING SAID PRESSURE RESPONSIVE SWITCH MEANS FOR ACTUATING SAID FIRST ELECTROMECHANICAL DEVICE TO CAUSE THE PUMP TO CONTINUE TO DELIVER FLUID UNDER PRESSURE FROM SAID FIRST PORT WHEN THE LOAD RESPONSIVE SWITCH MEANS IS ACTUATED UPON DELIVERY OF FLUID UNDER PRESSURE FROM SAID FIRST PORT AND FOR DEACTUATING THE FIRST ELECTROMECHANICAL DEVICE TO STOP THE FLOW OF FLUID UNDER PRESSURE FROM SAID FIRST PORT WHEN THE PRESSURE AT SAID FIRST PORT DROPS AT THE COMPLETION OF A DRAWING OPERATION AS THE TRAILING END OF A WORKPIECE PASSES THROUGH SAID DIE, THIRD CIRCUIT MEANS FOR ACTUATING SAID SECOND ELECTROMECHANICAL DEVICE AFTER THE COMPLETION OF A DRAWING OPERATION TO CAUSE SAID PUMP TO DELIVER FLUID FROM SAID SECOND PORT AND THEREBY CAUSE THE DRAW CARRIAGE TO TRAVEL TOWARD SAID DIE, AND FOURTH CIRCUIT MEANS INCLUDING SAID SECOND LIMIT SWITCH DEVICE FOR ACTUATING SAID THIRD ELECTROMECHANICAL DEVICE AS THE DRAW CARRIAGE APPROACHES THE DIE TO THEREBY DISCREASE THE RATE OF FLUID FLOW FROM SAID SECOND PORT AND REDUCE THE RATE OF TRAVEL OF THE DRAW CARRIAGE TOWARD THE DIE. 